You attach a file, press send, and one of two things happens. Either the mail app refuses on the spot, with an 'attachment too large' warning or classic Outlook's 'The file you're attaching is bigger than the server allows', or the message seems to go and a few minutes later a bounce arrives saying it was too large to deliver.
Neither means anything is broken. Email was designed to carry text, and every provider puts a ceiling on how big a single message can be. The part most people miss is that there are two ceilings, yours and the receiver's, and that the file grows by roughly a third on the way. So a message can pass your provider's check and still be refused at the other end. For anything big, the fix is almost always the same: send a link to the file instead of the file.
The real limits, from each provider's own help pages
These are the figures the providers publish themselves. They apply to the whole message, text and attachments together, not to each file separately. Work and school accounts are set by an administrator and can be higher or lower, and Google notes that its limits can change without notice.
- Gmail, personal account: 25 MB. Above that, Gmail removes the attachment and puts a Google Drive link in the email instead.
- Gmail on a Google Workspace work account: 25 MB to send (up to 50 MB on Enterprise Plus, in Gmail on the web only), measured before encoding. Receiving is up to 50 MB, or 70 MB on Enterprise Plus, measured after encoding.
- Outlook.com, including Hotmail and Live addresses: 25 MB per email, counting the text and everything inserted or attached. A OneDrive link does not count toward it.
- Classic Outlook for Windows (2013 and later) with a POP or IMAP account: Outlook itself stops at 20 MB of attachments by default, before your provider's limit even comes into play.
- Outlook with a Microsoft 365 work account: 35 MB to send and 36 MB to receive by default. Administrators can set anything from 1 MB to 150 MB.
- Outlook on a company's own Exchange server: 10 MB by default, set by the IT team.
- Yahoo Mail: 25 MB for all attachments in one message combined, for incoming and outgoing mail alike.
- iCloud Mail: 20 MB for incoming and outgoing messages, or up to 5 GB when Mail Drop is used.
Why it bounced when you were under the limit
Your provider only decides whether it is willing to send the message. Whether it arrives is up to the receiving server, which applies its own limit and has no idea what yours was. Send a 22 MB file from Gmail to someone on iCloud Mail and Gmail is perfectly happy, but iCloud's limit is 20 MB, so the message comes back. The same happens with a company mailbox whose IT team has left the limit at 10 MB.
The second reason is encoding. Attachments are converted into text before they travel, and that makes them bigger. Microsoft's documentation puts the increase at 33 percent; Google's says about 37 percent. Google's own figures show the effect: its Workspace sending limit is measured before encoding but its receiving limit after, so the 50 MB a Workspace mailbox can receive is roughly 36 MB of actual files. Outlook on the web allows for the same thing by letting you send only three quarters of the configured limit, so a 100 MB setting means 75 MB in practice.
Third, the attachment is not the only thing in the message. The text, a signature with a logo, and a long reply thread full of pasted screenshots all count toward the same ceiling.
A rule of thumb follows from those numbers. About 15 MB of files becomes roughly 20 MB once encoded, which is the smallest of the consumer limits above. Under that, an attachment will usually arrive anywhere. Over it, or when you do not know what the other person uses, send a link.
Gmail: let it turn the file into a Drive link
In personal Gmail you barely have to do anything. Attach a file over 25 MB and Gmail removes it from the message and inserts a Google Drive link in its place. The file is stored in your Drive, so it uses your Google storage, which is shared with Gmail and Google Photos.
To choose this yourself, or to send something already in Drive, use the Drive button in the compose window. The link keeps working until you delete the file or stop sharing it, so tidy up anything sensitive afterwards.
- Click 'Compose', then the Drive icon at the bottom of the message ('Insert files using Drive').
- Pick the file and choose 'Drive link' rather than 'Attachment'. 'Attachment' puts a copy inside the email, which brings the size limit straight back.
- Click 'Insert', then send. If the recipient cannot open the file, Gmail stops and asks you to change its sharing settings first.
- Choose 'Anyone with the link' if the person may not have a Google account; they do not need one to open a file shared that way. Pick view-only unless you want them editing your copy.
Outlook: upload it to OneDrive and send the link
Outlook does the same job with OneDrive. On Outlook.com a OneDrive link does not count toward the 25 MB email limit, and the linked file can be up to 2 GB.
If classic Outlook shows 'The file you're attaching is bigger than the server allows. Try putting the file in a shared location and sending a link instead', that is either Outlook's own 20 MB default for POP and IMAP accounts or, at work, the limit on your Exchange server. Microsoft documents a registry value, MaximumAttachmentSize, that raises Outlook's own check, but it cannot raise the limit on your provider's server or the receiver's, so the link is the better fix.
The menus differ between the versions of Outlook:
- Outlook.com and Outlook on the web: 'Attach', then 'Attach file', then 'OneDrive'. Choose the file and select 'Next'.
- New Outlook for Windows: 'Attach File', then 'Browse This PC'. Select the small arrow next to the attachment and choose 'Upload to OneDrive'.
- Classic Outlook: 'Attach File', then 'Browse Web Locations' for a file already in OneDrive, or attach it from your PC and use the arrow next to it, then 'Upload' and 'OneDrive'.
- In any version, use 'Manage access' on the link to make it view-only if the recipient should not be editing your file.
Apple Mail and iPhone: Mail Drop
Apple's answer is Mail Drop, which works from Mail on the Mac, iPhone and iPad and from iCloud Mail on iCloud.com. When a message, attachments included, is bigger than your email provider allows, Mail offers to send the attachments with Mail Drop instead. The files go to iCloud and the recipient downloads them from there.
The limits are generous: attachments up to 5 GB, 1 TB of Mail Drop storage in total, and none of it counts against your iCloud storage. Each attachment expires after 30 days, so the recipient has a month to download it.
If Mail on the Mac never offers it, check 'Mail', 'Settings', 'Accounts', 'Account Information' and tick 'Send large attachments with Mail Drop'. Apple's own help also notes that delivery can still fail if the recipient's email app has a smaller message size limit, so if a Mail Drop message bounces, fall back to an ordinary download link.
Yahoo Mail: share from Google Drive or Dropbox
Yahoo Mail's limit is 25 MB for all the attachments in a message together, and it applies to mail coming in as well as going out. For anything bigger, Yahoo's help points to the option in the attach menu to share files from Google Drive or Dropbox, which inserts a shareable link instead of the file itself. The file needs to be in one of those services first.
Yahoo also refuses some file types outright, such as .exe, .bat and .jar, whatever their size. A small file that will not attach may be a blocked type rather than a size problem.
Zipping: when it helps, and why it barely touches photos and video
Zipping is the first thing most people try, so it is worth knowing in advance whether it will work. A zip shrinks a file by squeezing out repetition. Documents, plain text, CSV exports and older uncompressed formats are full of it and can come out much smaller.
Photos, video and music are not. JPEG and HEIC photos, MP4 and MOV videos and MP3 audio are already compressed when they are saved, so there is almost nothing left to squeeze, and the zip ends up barely smaller than the originals. The same goes for modern Word, Excel and PowerPoint files, which are compressed internally already. Zipping a folder of holiday photos gives you one file instead of fifty, which is tidy, but not smaller.
A zip is still handy for bundling many files into one attachment. To make one, or to shrink photos properly:
- Windows: right-click the file or folder (on Windows 11 choose 'Show more options' first), then 'Send to', then 'Compressed (zipped) folder'.
- Mac: Control-click the file or folder and choose 'Compress'. Several items selected together become one file called Archive.zip.
- Photos in classic Outlook: attach them, go to 'File', then 'Info', and select 'Resize large images when I send this message'. In new Outlook, resizing a picture only changes how big it looks in the message, not its file size.
- Video: there is no honest shortcut. Exporting at a lower quality makes it smaller but looks worse, so a link is usually the right answer.
Send a download link instead
Every fix above ends in the same place: the file sits somewhere online and the email carries a link to it. You can do that directly with whatever you already use, such as Google Drive, OneDrive, Dropbox or iCloud Drive, and paste the link into an ordinary email. A link is one line of text, so it gets through every size limit, including the one at the receiving end that you cannot see.
If you would rather not put the file in your own cloud drive, a transfer link does the same job and cleans up after itself. OneSol Send (onesol.io/send) is one option: upload up to 5 GB, get one link; the link and files are deleted after 24 hours, and the person receiving needs no account (you need a free OneSol account to send). The 24-hour window suits a file someone will download today, not one they need to come back to next month.
Whichever you use, check two things before you send: that the link opens in a private browser window where you are not signed in, because that is how the recipient will see it, and that it is view-only unless you meant otherwise.